Capacitation is a poorly understood process occurring in mammalian sperm prior to the acrosome reaction; it is an essential preliminary to fertilization. The objective of the proposed research is to explain the nature of surface changes occurring in guinea pig, hamster, rabbit, and human sperm during capacitation and to examine the mechanims which affect these changes. A new approach using plant lectins to study the sperm surface is proposed. A simple, reliable assay was developed to quantitate the lectin-induced agglutinability of sperm. This assay was used to show that capacitated sperm are more agglutinable by certain lectins than uncapacitated sperm. Moreover, this increase in agglutinability can be induced in uncapacitated sperm by trypsinization and can be prevented during capacitation by at least 2 trypsin inhibitors. The proposed work is designed to first determine if an increase in lectin induced agglutinability is a "general" feature of capacitation in 4 representative species. Second, we will attempt to explain why lectin-induced agglutinabiluty increases during capacitation. Ultrastructural localization of ferritin conjugated lectins will be used to determine if there is an increase in the number and/or mobility of lectin receptors on the surface of capacitated sperm. Finally, our preliminary data support the idea that a trypsin-like enzyme modifies the sperm surface during capacitation. Experiments are planned using trypsin inhibitors to test this idea. Potentially, these studies will: 1. provide a new, direct assay for capacitation, 2. clarify mechanisms involved in capacitation, and 3. establish if a trypsin-like enzyme acts in capacitation.